The present invention relates to forged alloys having a basic nickel-chrome-cobalt composition and further includes at least titanium and aluminum as additional components for the purpose of producing a coherent phase that is achieved by thermal treatment for structural hardening. In this context, the expression "forged alloy" is intended to include those alloys which are subjected to plastic deformation at varying temperature levels for the purpose of forming the desired metal products. For example, such plastic deformation may be achieved by hammering, welding, molding, rolling and other similar and well known metallurgical techniques.
The field of alloys to which the invention pertains includes practically no iron except for that amount which is included or occurs as residual impurity. These alloys are particularly characterized by their resistance to oxidation and corrosion under heat conditions because of the chrome and aluminum constituents in the basic composition. A high cobalt content is also desirable for these alloys for the purpose of imparting forgeability under the application of heat. It is further advantageous if these alloys include titanium, aluminum, molybdenum and/or tungsten since these elements contribute in conferring significant mechanical properties to the alloys at temperatures up to approximately 850.degree. C. or such temperatures up to which these elements occur in solid solution within the nickel-cobalt-chrome matrix. In consideration of appropriate thermal treatment, the most significant factor of alloy hardening is the presence of the gamma prime phase of the cubic molecular arrangement of the structure Ni3(Ti,Al), which structure is precipitated by thermal treatment and in which structure cobalt and chrome may substitute for part of the nickel.
Because such alloys are resistant to corrosion and oxidation under heat conditions, exhibit good creep behavior and possess outstanding mechanical properties under temperature conditions between 500.degree. and 1000.degree. C., they are utilized to produce forged products for a variety of high temperature applications, such as turbines for the aircraft and similar industries. However, such known alloys normally undergo a significant loss of ductility at a temperature range of from 650.degree.-800.degree. C. This loss corresponds to a low in the curve of elongation at rupture as a function of temperature, the minimum of which can be at less than 1%. This disadvantage necessitates the implementation of various precautions during the forging or similar mechanical operations, thereby limiting the applications of such alloys.